tony83

hi, i need some help. ive got a 94 cherokee 4.0 that runs horrible... i have to throttle it to get it started then have to keep it running for a minute before it will even idle. once its running it runs very rough, sounds like its missing/studdering when i try to rev it up it stumbles and backfires and wont get past 1500rpm... here is a list of things that have been replaced/checked since this started... fuel pressure-good, sparking on all six, new plugs and wires new coil, new distributor cap, six month old cps, wiring harness is firing all injectors, unplugged map sensor and it ran worse, checked tps it was saying .79v closed and 3.86 wide open, checked for vacuum leaks, both new water temp sensors, new air temp sensor, and local mechanic checked the timing chain and said it was good plus its not making noise (although it is running like it has jumped timing) i have turned the distributor both ways just to see what would happen and its not a tooth off (there was another guy working on it before i started)
sorry for the lengthy explanation any help will be greatly appreciated

tony83

i also let it run for a few seconds then shut it off and touched all the exhaust primaries.. they where all about the same temp so i assume it is not only one or two cylinders causing the problem. also the pcm is showing no error codes

Gee oh Dee

Fuel filter clogged?

tony83

it holds good fuel pressure while running and trying to rev it up...

tony83

compression test checks out good

tjwalker

*Assuming that fuel pressure (31 psi) was verified with a known good gauge? Anything less than a gauge reading is pure guesswork

*Did you perform a full test on that throttle position sensor? That sensor is still suspect here for these symptoms. They aren't particularly expensive.

*Cleaning engine grounds is NEVER a bad idea. Bad grounds are the cause of many gremlins.

*If that distributor was EVER removed, distributor indexing is still a possibility here.

golfmiser

I know you checked the vacuum lines but I would double check the small hard plastic line coming from the map sensor. I had one that rubbed against something and caused the air leak.

tony83

if i get a decent break in the rain today i will inspect and clean the grounds (cant believe ive over looked that so far) the tps sensor was checked within range and it had no erratic jumps in voltage through out its travel... the distributor has been checked twice at tdc number 1 compression stroke the rotor button points right at number 1 and rotating it either way from the stock position (which is a fixed position) only results in it running worse... thus it has to be in the correct placement... also i will re-check the vacuum to the map sensor i will also re-check the intake manifold its self for leaks... also the fuel pressure gauge is brand new i will check it against my camaro with a known fuel pressure... great advice guys thanks for the help so far ill let yall know how it gos